Synthesis of functionalized spiro[indanone-benzazepine] scaffolds via [4 + 3] annulation reaction of N-(o-chloromethyl)aryl amides with ninhydrin-derived Morita−Baylis−Hillman carbonates

Substrate-controlled [4+1] and [3+2] annulations of ninhydrin-derived Morita–Baylis–Hillman carbonates to access polysubstituted furans and cyclopentenes

“…On the basis of our experimental results and previous reports, 5,11–13 a plausible mechanism is depicted to explain the reaction process in Scheme 3. Firstly, DMAP as a nucleophilic Lewis base attacks MBH carbonate 2a, generating CO 2 and a tert -butoxide anion, which could grab a hydrogen to form nitrogen ylide intermediate A .…”

“…Notably, it still is highly desirable to find suitable reaction partners for β-regioselective [4+1]-annulation of MBH carbonates as substrates, further expanding the chemical space of MBH carbonates. Therefore, in connection with our continuous efforts on the annulation of MBH carbonates, 13 we would like to present the β-regioselective [4+1] cycloaddition of ninhydrin-derived MBH carbonates with α,β-unsaturated ketones to efficiently construct polysubstituted furans incorporating indane-1,3-dione motifs under mild reaction conditions without metal catalysts (Scheme 1d), which are structurally interesting cores with potential in natural product synthesis and drug discovery. In contrast, the polysubstituted cyclopentenes bearing dispiro-bisindanedione motifs were also obtained via β-regioselective [3+2] annulations by switching enone analogues under the same catalytic conditions (Scheme 1d).…”